1. Field of the Invention
The present invention relates to a pipe joint for use in the piping of a hydraulic circuit including hydraulic apparatus and, more specifically, to a pipe joint effective for properly attaching an elbow to a hydraulic apparatus.
2. Description of the Prior Art
Referring to FIG. 13 showing a conventional washer-faced 90 degree elbow, the body 41 of the elbow has one end provided with a threaded portion 42 for screw engagement with a pipe and the other end provided with a threaded portion 43 for screw engagement with a hydraulic apparatus 47. In attaching the elbow to the hydraulic apparatus 47, the threaded portion 43 is screwed in a connection port 48 by a predetermined depth, the direction of the elbow is determined, and then, a locknut 44 is screwed down firmly against a backup washer 45 to fix the elbow in place. When the locknut 44 is screwed down, an O ring 46 is squeezed flat so as to be in close contact with the outer circumference of the body 41, the backup washer 45 and the inner surface of the connecting port 48 of the hydraulic apparatus 47 for sealing.
As mentioned above, since a conventional pipe joint is attached fixedly to the hydraulic apparatus 47, it is possible that leakage occurs due to the loosening of the pipe joint relative to the hydraulic apparatus 47 or the loosening of connection between the pipe joint and a pipe caused by the vibration of the pipe or the like if the direction of the pipe joint is not determined properly taking into consideration the handling of the pipe, and the movement and vibration of the pipe.
In screwing the elbow of FIG. 13 in the hydraulic apparatus 47, a cylindrical space of a radius l (FIG. 13 ) must be secured around the elbow. Therefore, in connecting a plurality of pipes to a hydraulic apparatus, such as an oil control valve provided on a forklift truck, in a limited space, some measures, such as attaching pipe joints in different heights, must be taken to avoid interference between the adjacent pipe joints. Therefore, in attaching conventional washer-faced elbows to a hydraulic apparatus, a sufficiently large space must be secured on the hydraulic apparatus and an appropriate method of attaching the pipe joint must be contrived. Thus, the conventional pipe joint is disadvantageous in collectively arranging a plurality of pipe joints, in arranging a plurality of pipe joints in a narrow space and removing some of a plurality of pipe joints from the hydraulic apparatus for replacement. Furthermore, since the O ring 46 is squeezed and the backup washer 45 must slide smoothly relative to the body 41 of the elbow in screwing down the locknut 44, the inside diameter of the backup washer 45 and the outside diameter of the O ring groove formed in the circumference of the body 41 must be finished in a considerably high accuracy, which is disadvantageous in manufacturing the elbow.